<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <!-- 3.1引入外部样式表 -->
    <!-- <link rel="stylesheet" href="./outer.css"> -->
    <!-- 1.内部样式表 -->
    <style>
        /* 3.2@import引入 放在style标签第一行 */
        @import url(./outer.css);
        div{
            width: 100px;
            height: 100px;
        }
    </style>
</head>
<body>
    <!-- 2.内联样式/行内样式 -->
    <div style="color: red;">块级元素</div>
</body>
</html>